1. Field of the Invention
The invention relates to radiation dosimetry using a nanocrystalline thermoluminescent phosphor in an inorganic, light transparent matrix. More particularly, the invention relates to thermoluminescence radiation dosimetry using a particulate, nanocrystalline phosphor, such as ZnS:Cu dispersed in a light transparent glassy matrix, which luminesces when heated (i.e., raised to a temperature above the ambient working temperature of the dosimeter) after being irradiated with UV or ionizing radiation.
2. Background of the Invention
Radiation dosimetry using thermoluminescent phosphors which accumulate and store energy when exposed to ionizing radiation and release the energy as luminescence when heated are simple, compact, reliable and relatively easy and inexpensive to use. This technology is extensively used for monitoring exposure to ionizing radiation, such as gamma and X-rays, in applications such as personnel protection, environmental monitoring and radiotherapy. Thermoluminescent dosimetry is based on the ability of a material exposed to ionizing radiation to absorb a portion of the ionizing radiation energy with a resultant promotion of valence band electrons to the conduction band of the material. Electrons in the conduction band migrate to trap sites that are energetically near, but below the conduction band energy. These trapped electrons remain trapped for extended periods of time. They can be promoted and released into the conduction band by thermal energy. Once in the conduction band the electrons migrate and recombine radiatively with trapped holes to release energy in the form of electromagnetic radiation in the visible light spectrum. The amount of light energy released by heating is related to the ionizing radiation exposure experienced by the material.
Thermoluminescent materials presently in use are particulate, inorganic, crystalline materials and are referred to as phosphors due to their ability to emit visible light radiation when suitably excited. These thermoluminescent phosphor materials are chips or microcrystalline size powders which are opaque and highly light scattering. This means that light generated within a layer of such phosphor particles has a smaller probability of reaching a photon detector than does light generated near the surface. The ideal thermoluminescent dosimeter material would be light transparent and have radiation collecting and light emitting ability which is a function of mass. The thermoluminescent properties of glasses, such as sodium silicate and alkali borate glasses and quartz doped with germanium, aluminum and copper sulfate, have been studied. However, none of the glass compositions studied have been found suitable for use in thermoluminescence radiation dosimetry. Therefore, it would be a significant improvement to the art if a thermoluminescent glass or glassy material could be found which is optically transparent and has the high sensitivity and long storage times of the crystalline thermoluminescent materials.